Surgical Bur With Non-Paired Flutes

ABSTRACT

A surgical dissection tool for cutting bone and other tissue includes a cutting head having an outer surface having non-paired or an odd number of flutes formed therein. Each flute includes a rake surface intersecting with the outer surface to form a cutting edge, and a relief surface opposite the rake surface. The relief surface and the rake surface form a first angle. Each flute also includes a leading angled surface extending from the relief surface to a distal end portion of the cutting head, the leading angled surface and the rake surface forming a second angle substantially the same as the first angle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/992,400 filed Jan. 11, 2016, which is a divisional of U.S. patentapplication Ser. No. 13/447,372 filed on Apr. 16, 2012, now U.S. Pat.No. 9,232,952 issued on Jan. 12, 2016. The entire disclosures of theabove applications are incorporated herein by reference.

FIELD

The disclosure is directed to a surgical system for bone cutting orshaping and more particularly, to a surgical dissection tool of thesurgical system.

BACKGROUND

During surgical procedures using cutting tools, surgeons often balanceaggressiveness of cutting tools with the ability to precisely controlthe cutting tool. As a surgeon controls the cutting instruments toincrease aggressiveness, potentially decreasing the time period of thesurgical procedure, the surgeon may have less precise control. Whilenon-aggressive cutting may be more precise, it may increase the timeperiod of the surgical procedure.

A part of the reduced precision during aggressive cutting may be theresult of tool chatter. Tool chatter may occur for several reasons. Onereason is the spacing of the flutes. A cutting tool with “paired” flutesor an even number of flutes may chatter as a result of one cutting edgeengaging tissue at the same time that another cutting edge isdisengaging from tissue or may manifest when the cutting depth ofmultiple engaged flutes vary, producing asymmetric forces. In addition,tool chatter may result from an inability of tissue in the flutes toexit the flute before the flute reengages tissue. This may be compoundedduring aggressive cutting that can result in relatively large slices oftissue.

The present disclosure is directed to a surgical system for bone cuttingor shaping addressing one or more of the limitations in the prior art.

SUMMARY

In one exemplary aspect, the present disclosure is directed to asurgical dissection tool for cutting bone and other tissue. Thedissection tool may include a distal end portion and a proximal endportion. A shank may extend between the distal end portion and theproximal end portion. A cutting head disposed at the distal end portionconnects to the shank. It has an outer surface having an odd number offlutes formed therein. Each flute includes a rake surface intersectingwith the outer surface to form a cutting edge, and a relief surfaceopposite the rake surface. The relief surface and the rake surface forma first angle. Each flute also includes a leading angled surfaceextending from the relief surface to a distal end portion of the cuttinghead, the leading angled surface and the rake surface forming a secondangle substantially the same as the first angle.

In one aspect, the odd number of flutes comprises three flutes. Inanother aspect, the first and second angles are obtuse angles. Inanother aspect, the leading angled surface comprises one of a chamferand a round. In another aspect, the flute further comprises a bevelbetween the leading angled surface and the rake surface.

In another exemplary aspect, the present disclosure is directed to asurgical dissection tool for cutting bone and other tissue that includesa shank and a cutting head connected to the shank. The cutting head andshank have a central longitudinal axis, and the cutting head has anouter surface having an odd number of flutes formed therein. Each flutemay include a planar rake surface intersecting with the outer surface toform a cutting edge and may include a planar relief surface opposite therake surface. The planar rake surface and the planar relief surface forman obtuse angle. A leading angled surface may extend from the planarrelief surface to a distal end portion of the outer surface, and theleading angled surface of at least one of the flutes includes adistal-most end extending past the longitudinal axis.

In another exemplary aspect, the present disclosure is directed to asurgical dissection tool for cutting bone and other tissue that includesa shank and a cutting head connected to the shank. The cutting head andshank may have a central longitudinal axis and an outer surface. Theouter surface may be substantially spherically shaped and may have threeflutes formed therein. The outer surface between adjacent flutes of thethree flutes forms an angle within a range of about 45-55 degrees. Eachflute of the three flutes includes a planar rake surface intersectingwith the outer surface to form a cutting edge. The planar rake surfaceis parallel to and offset from a reference plane through thelongitudinal axis. Each flute also includes a planar relief surfaceopposite the rake surface and intersecting with the outer surface. Theplanar relief surface may extend to a proximal portion of the cuttinghead, the planar rake surface and the planar relief surface may form afirst obtuse angle within a range of about 95 and 105 degrees. A leadingangled surface may extend from the planar relief surface to a distal endportion of the outer surface. The leading angled surface and the planarrelief surface may form a second angle substantially the same as thefirst obtuse angle. The leading angled surface of at least one of thethree flutes may include a distal-most end extending past thelongitudinal axis.

In another exemplary aspect, the present disclosure is directed to asurgical system having a surgical dissection cutter assembly with asurgical dissection tool as described herein.

DRAWINGS

The A more complete understanding of the present disclosure andadvantages thereof may be acquired by referring to the followingdescription taken in conjunction with the accompanying figures.

FIG. 1 is an illustration of a surgical dissection cutter assemblyaccording to the present invention use in a human patient.

FIG. 2 is an illustration of partially exploded perspective view of asurgical dissection cutter assembly including a driver and a surgicaldissection tool according to the present invention.

FIG. 3 is an illustration of an isometric view of a distal end of asurgical dissection tool according to one exemplary aspect of thepresent disclosure.

FIG. 4 is an illustration of a side view of a surgical dissection toolaccording to one exemplary aspect of the present disclosure.

FIG. 5 is an illustration of an end view of a distal end of a surgicaldissection tool according to one exemplary aspect of the presentdisclosure.

FIG. 6 is an illustration of a side view of a distal end of a surgicaldissection tool according to one exemplary aspect of the presentdisclosure.

FIG. 7 is an illustration of another side view of a distal end of asurgical dissection tool of FIG. 6, rotated from the position in FIG. 6according to one exemplary aspect of the present disclosure.

FIG. 8 is an illustration of an end view of a distal end of a surgicaldissection tool according to one exemplary aspect of the presentdisclosure.

FIG. 9 is an illustration of an isometric view of a distal end of asurgical dissection tool according to another exemplary aspect of thepresent disclosure.

FIG. 10 is an illustration of a side view of a surgical dissection toolaccording to one exemplary aspect of the present disclosure.

FIG. 11 is an illustration of another side view of a surgical dissectiontool according to one exemplary aspect of the present disclosure,rotated from the side view shown in FIG. 10.

FIG. 12 is an illustration of an end view of a distal end of a surgicaldissection tool according to one exemplary aspect of the presentdisclosure.

FIG. 13 is an illustration of an end view of a distal end of a surgicaldissection tool as it relates to bone tissue cutting a path in thetissue according to one exemplary aspect of the present disclosure.

DETAILED DESCRIPTION

Reference is now made in detail to exemplary embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers are usedthroughout the drawings to refer to the same or like parts.

The present disclosure is directed to a surgical dissection cutterassembly including a dissection tool driver that drives a surgicaldissection tool during surgical procedures. The dissection tool mayprovide increased cutting control and cutting precision by reducing theincidence of chatter during cutting. This may permit a surgeon to makemore aggressive dissections without compromising control and cuttingprecision. In turn, this may reduce the length of time required for somesurgical procedures, benefitting the patient. In addition, reducedchatter may result in smoother cuts, which may increase healing andreduce recovery times.

The exemplary dissection tool disclosed herein is a surgical bur havingnon-paired flutes. As such, the flutes themselves are not spacedprecisely 180 degrees apart. The offset flutes appear to provide abenefit of reduced chatter while still permitting relatively aggressivecutting. The advantage may derive from the offset in timing between thetime one flute engages to cut tissue as another disengages the tissueduring a single revolution of the dissection bur.

FIG. 1 shows a human patient A undergoing a neurological operation. Asis common practice, access to the brain or other neurological structuresoften requires delicate dissection of bone and other tissues to gainaccess. By way of example, a dissection cutter assembly employing adissection tool driver 10 in accordance with one aspect of the presentinvention is shown being utilized to dissect a portion of patient A'sbone and other tissue adjacent to the surgical access site.

FIG. 2 illustrates the dissection tool driver 10 for the dissection ofbone or other tissue in greater detail. The dissection tool driver 10includes a motor housing 12, coupled to an air supply and hose assembly14 that supplies pressurized air to a motor in the motor housing 12 andvents the low pressure exhaust air away from the surgical site. Thedissection tool driver 10 further includes an attachment housing 16 thatconnects to a dissection tool 100. The dissection tool 100 is describedin greater detail with reference to FIGS. 3-5.

FIG. 3 shows an isometric view of a distal end portion, FIG. 4 shows aside view of the dissection tool 100, and FIG. 5 shows an end view ofthe distal end portion. Referring to these figures, the dissection tool100 is, in this example, a surgical bur that includes a proximal endportion 102 and a distal end portion 104 connected by an extending shankor shaft 106. The shank 106 has a longitudinal axis 108 defining acenterline of the proximal end portion 102 and the distal end portion104. In one embodiment, the shank 106 includes a diameter within a rangeof about 0.030-0.150 inch.

The proximal end portion 102 is arranged to engage with and be driven bya shaft in the motor portion 12, but passes through and is supported bythe attachment housing 16 in FIG. 2. In this example, the proximal endportion 102 includes a first non-circular region 112 when viewed incross-section, a second non-circular region 114 when viewed incross-section, and an intermediate region 116. In this example, thefirst and second non-circular regions 112, 114 are shown as hex-shapedsurfaces and have the same cross-sectional shape. These regions areconfigured to engage with a driving portion of the dissection tooldriver 10. The intermediate region 116 has a smaller cross-sectionalarea than the first and second non-circular regions 112, 114. It may beused to engage with or be engaged by the dissection tool driver 10 toanchor or otherwise secure the dissection tool 100 in the dissectiontool driver 10. In this example, the intermediate region 116 is has acircular cross-section with a diameter smaller than the smallestcross-sectional width of the first non-circular region 112.

The distal end portion 104 includes a cutting head 120 connected to theshank 106. The transverse cross-section of the cutting head 120 isgreater than the diameter of the shank 106. The cutting head 120 isshown as a surgical cutting bur with an outer surface 122. In thisexample, the outer surface 122 is substantially spherically shaped. Inother embodiments, the cutting head 120 may have a cross-section smallerthan at least a portion of the shank 106. In one embodiment, the shank106 includes a neck with a curved or tapered surface that extends to thecutting head 120.

The cutting head 120 is formed with three symmetric cutting flutes 124formed into the outer surface 122 and evenly spaced about the cuttinghead 120. Each cutting flute 124 includes a rake surface 126 forming acutting edge 128 with the outer surface 122, and includes a reliefsurface 130 adjacent the rake surface 126. A distal region of thecutting head 120 includes a leading angled surface shown as a chamferportion 132 leading to the relief surface 130. A bevel 134 connects thechamfer portion 132 to the rake surface 126. As can be seen, the cuttingedge 120 forms a smooth arc from the distal-most portion of thespherical cutting head 120 to the proximal side of the cutting head 120.

In this example, the rake surface 126 is a planar surface across itslength. Here, the rake surface 126 is offset from but parallel to aplane passing through the longitudinal axis 108. Accordingly, the rakesurface 126 lies in a plane that does not intersect the center-line orlongitudinal axis 108 of the dissection tool 100. While shown as beingoffset after the centerline, in other embodiments, the rake surface 126is offset from but parallel to a plane before or in front of a planepassing through the longitudinal axis to impart a desired rake angle. Inone embodiment the rake surface is disposed so that a plane through therake angle intersects the axis for a neutral rake angle. Although shownas planar, in other embodiments, the rake surface 126 surface is angledor formed by a helix.

The relief surface 130 forms the opposing side of the flute 124 and,together with the rake surface 126, forms an angle .theta. within arange of about 85-120 degrees, although additional angles arecontemplated. In one embodiment, the angle .theta. is within a range ofabout 95-105 degrees and in another embodiment, the angle is about 100degrees. The relief surface extends from the chamfer portion 132 to aproximal portion of the cutting head 120. Different embodiments of thedissection tool 100 include angles between the rake surface 126 and therelief surface 130 that are acute, right or obtuse. In some embodiments,the angle .theta. is within the range of about 90.degree. and100.degree.

As best seen in FIG. 4, the chamfer portion 132 angles from the reliefsurface 130 to a distal end of the cutting head 120. In the exampleshown, the chamfer portion 132 is cut at an angle a measured from a linetraverse to the axis 108 to fall between about 20 and 70 degrees. In oneexample, the chamfer portion 132 is formed with an angle .alpha. betweenthe range of about 35-45 degrees, and in one example, the angle .alpha.is about 40 degrees. The angle .alpha. is formed so that the end of thechamfer portion 132 extends past the centerline or axis 108, as can beseen in FIG. 4. In addition, in the embodiment shown, the chamferportion 132 is formed relative to the rake surface 126 to form an anglethat substantially corresponds to the angle .theta.0 formed between therelief surface 130 and the rake surface 126.

FIG. 5 shows how the bevel 134 intersects with the outer surface 122 ofthe cutting head 120 to form a leading surface with the outer surface122 at the distal most end of the cutting head. The bevel 134 angles thecutting edge 128 so that each flute 124 is independent of and does notintersect the other flutes, even though they each extend past thecenterline or axis 108. In the embodiment shown, the cutting head 120,albeit spherically shaped, includes a truncated proximal end that isbrazed to the shank 106.

FIGS. 6-8 show an additional embodiment of a dissection tool, referencedhere by the numeral 200. Some of the sizes, angles, and shapes offeatures of the dissection tool 200 are similar to those describedabove, and will not be repeated here. The dissection tool 200 includes ashank 206 and a proximal end similar to the shank and proximal enddiscussed above with reference to the dissection tool 100. Therefore,these will not be described further here.

The dissection tool 200 includes a cutting head 220 with a sphericalouter surface 222 having three cutting flutes 224 a-c formed therein,with each cutting flute 224 a-c having a respective planar rake surface226 a-c that intersects the outer surface 222 to form a respectivecutting edge 228 a-c. A relief surface 230 a-c forms an opposing wall toeach respective rake surface 226 a-c of each cutting flute 224 a-c. Asdescribed above, in one embodiment, the rake surfaces 226 are parallelto, but offset from a plane through the centerline or axis 208. In otherembodiments, the rake surfaces 226 form planes that pass through thecenterline or axis 208.

Instead of having identical flutes as disclosed with reference to thedissection tool 100, the dissection tool 200 includes cutting flutesthat vary from each other. In this example, each cutting flute 224 a-cincludes a respective leading angled surface shown as a chamfer or around 232 a-c extending from its most distal end to the relief surface230. The chamfers or rounds 232 a-c of each flute 224 a-c, however, havedifferent depths or curvatures. This can be understood with reference toFIG. 6 where each chamfer or round is different sized.

FIGS. 7 and 8 each show an illustration of a side view of the cuttinghead 220 showing the curvature along the different flutes of thedissection tool 200. FIG. 7 shows the profile of the relief surface 230a and the chamfer or round 232 a. FIG. 8 shows the profile of the reliefsurface 230 c and the chamfer or round 232 c. As can be seen bycomparison, the chamfer or round 232 a in FIG. 7 is substantially largerthan the chamfer or round 232 c in FIG. 8. As can be seen in FIG. 7, theleading angled surface comprises both a chamfer and a round. The roundconnects the chamfer and the relief surface 230 a. Furthermore, the rakesurface 228 continues the full length of the relief surface 230 and thechamfer or round 232. That is, the dissection tool 200 does not includea bevel surface. However, since the chamfer or round 232 varies by flutein the exemplary tool 200, the surface area of the rake surface alsovaries from flute to flute. As can be seen by comparing FIGS. 7 and 8,the area of the rake surface 226 a is greater than the area of the rakesurface 226 c. Similarly, the length of the cutting edge varies fromflute to flute, and the cutting edge 228 a is greater than that of thecutting edge 228 c. In addition, chamfer or round 232 a in the cuttingflute 224 a extends past the centerline or axis 208 as shown in FIG. 7,while the cutting flutes 224 b and 224 c do not extend past thecenterline or axis 208.

FIGS. 9-12 show an additional embodiment of a dissection tool,referenced here by the numeral 300. Some of the sizes, angles, andshapes of features of the dissection tool 300 are similar to thosedescribed above, and will not be repeated here. The dissection tool 300includes a shank 306 and a proximal end similar to the shanks andproximal ends discussed above.

The dissection tool 300 includes a cutting head 320 with an outersurface 322 having three cutting flutes 324 formed therein, with eachcutting flute 324 having a respective rake surface 326 that intersectsthe outer surface 322 to form a respective cutting edge 328. Here, thecutting flutes 324 are substantially identically shaped and therefore,are all referred to by the same reference numeral.

In this embodiment, the rake surface 326 is helix shaped, with a leadingportion 340 and a trailing portion 342. The helix angle increases theeffective shearing action thus reducing cutting forces and the amount ofheat generated during the bone cutting process. Chip ejection also maybe improved. During cutting, as the bur rotates about the longitudinalaxis 308, the leading portion 340 is the first portion to engage thebone tissue during a cutting action and the trailing portion 342 followsthe leading portion 340. This may provide additional stability duringcutting to the three-flute bur because resistance from the bone tissueis applied through a progressive siding action. This makes the cuttingforces more constant with less chance for chatter. Instead of the wholecutting edge of a flute engaging the bone at once, the helix makes theleading portion 340 engage the bone first, and the remainder of thecutting edge engages bone over a very short period of time. This reducesboth vibration and dampening, resulting in greater levels of stability.

In this embodiment, the leading portions 340 of the respective rakesurfaces 326 are parallel to, but offset from a front of a plane throughthe centerline or axis 308. In other embodiments, the leading portions340 of the rake surfaces 326 form planes that pass through thecenterline or axis 308 or that are behind a plane through a centerlineor axis 308. As can be seen in FIG. 12, the leading edge extends infront of and past the centerpoint.

FIG. 12 shows an end view of the dissection tool 300 with a referenceboundary 346 creating a circle that intersects the cutting edges 328 ofthe dissection tool 300. Although shown in cross-section as a line, inone example, the reference boundary 346 is a spherical boundaryinteresting the cutting edges 328. The cutting edges 328 of thedissection tool 300 intersect with the spherical reference boundary 346.However, in cross-section, the outer surface 322 gradually tapersinwardly from the reference boundary 346. As can be seen in FIG. 12, theouter surface 322 includes a tapered portion 348 followed by a curvedportion 350. The tapered portion 348 extends from the cutting edgerearward along the outer surface 322. The tapered portion 348 isfollowed by a curved portion 350 that is formed with a changing radiusas an Archimedes spiral or a cam surface. The cam relief formed as aresult of the tapers portion and the curved portion 350 is labeled withthe reference numeral 351. This provides the greatest clearancepermitting the bur to advance into the bone tissue without excessiveinterference from the outer surface 322 engaging the newly cut surface.This can help reduce heating that may occur if the outer surface were tobe engaged with or rubbing on the bone tissue.

A relief surface 330 forms an opposing wall to each respective rakesurface 326 of each cutting flute 324. In the embodiment of thedissection tool 300, the flutes 324 are all substantially identical, andare similar to the rake surfaces described above. A reference line 352identifies a web thickness of the cutting head 320. The web thickness isthe minimum diameter of the solid portion of the cutting head. Whenusing three flutes as shown in FIG. 12, the web thickness has a radiusequal to about half of the radius to the cutting edges 328. Otherembodiments have a web thickness that is either higher and lower. In oneembodiment, the web thickness radius is within a range of about 40% to80% of the radius to the cutting edges 328.

FIGS. 10-11 each show an illustration of a side view of the cutting head320 showing the curvature along the different flutes of the dissectiontool 300. FIG. 10 shows the profile of the relief surface 330 c and thechamfer or round 332 c. FIG. 11 shows the profile of the rake surface326 and the cutting edge 328. As can be seen by comparison, the rakesurface 328 forms a helix that extends from the leading portion 340 tothe trailing portion 342.

FIG. 13 shows the exemplary surgical dissection tool 300 in a cuttingenvironment. In this view, a bottom view of the cutting tool 300 cuts apath in bone tissue structure 370, with the bone tissue structure 370being transparent in order to display the cutting tool.

In FIG. 13, the cutting edge 328 of the dissection tool 300 is shownengaged in and cutting material from the bone structure 370. The cuttingedge 328 is also just engaging into the bone structure 370. As can beseen, at this point in time, there are only two cutting edges 328engaged in the bone structure 370. The third cutting edge 328 moved outof engagement with the bone structure. Because the flutes are offset andnot directly across from each other, the cutting edge 328 moves out ofcontact with the bone structure before the cutting edge 328 engages thebone structure. The time differential between the time one cutting edgeengages tissue and a separate cutting edge disengages the tissue duringa single revolution of the dissection bur may provide advantages indecreased chatter. Accordingly, at any single point in time, only twoout of the three cutting edges are in contact with the bone structure.

Although the exemplary dissection tools are burs with three flutes, thedissection tools may have additional non-paired flutes. For example, oneexample of the dissection tool includes five flutes. In use, the oddnumber of flutes may result in a reduced level of chatter during bone orcutting. Since cutting occurs by rotating the dissection tool about itslongitudinal axis, the odd number of flutes offsets the timing ofinitial cutting edge engagement and cutting edge disengagement. Thisoffset in timing is thought to reduce the incidence of chatter whilestill permitting aggressive cutting action. Furthermore, since at leastone of the flutes has a cutting edge that extends past the longitudinalaxis or centerline, the angle that the cutter is held at by the surgeonis not as critical as it might otherwise be.

It is evident that the particular illustrative embodiments disclosedabove may be altered or modified and all such variations are consideredwithin the scope and spirit of the present invention.

What is claimed is:
 1. A surgical dissection tool for cutting bone andother tissue, comprising: a shank; and a cutting head extending from theshank, the cutting head and the shank having a central longitudinalaxis, the cutting head having an outer surface with an odd number offlutes formed therein, each flute comprising: a rake surfaceintersecting the outer surface to form a cutting edge; a relief surfaceopposite the rake surface; and a leading angled surface extending fromthe relief surface to a distal end portion of the outer surface; whereina first rake surface of a first flute has a first surface area and asecond rake surface of a second flute has a second surface area, thefirst surface area different from the second surface area.
 2. Thesurgical dissection tool of claim 1, wherein the odd number of flutesconsists of three flutes.
 3. The surgical dissection tool of claim 1,wherein each rake surface is planar.
 4. The surgical dissection tool ofclaim 1, wherein at least one rake surface is parallel to, but offsetfrom a plane through the central longitudinal axis.
 5. The surgicaldissection tool of claim 1, wherein at least one rake surface extendspast the central longitudinal axis.
 6. The surgical dissection tool ofclaim 1, wherein the leading angled surface comprises at least one of achamfer and a round.
 7. The surgical dissection tool of claim 1, whereinthe outer surface is spherically shaped.
 8. The surgical dissection toolof claim 1, wherein an end view of the dissection tool defines areference boundary that intersects the cutting edge and a cam surfaceforms a cam relief between the cam surface and the reference boundary.9. The surgical dissection tool of claim 2, wherein the three flutesinclude three cutting edges, wherein during cutting at any single pointin time, only two out of three cutting edges are in contact with thebone.
 10. The surgical dissection tool of claim 1, wherein a length ofthe cutting edge of each of the flutes differs among the flutes.
 11. Thesurgical dissection tool of claim 1, wherein a first leading angledsurface of the first flute extends past the central longitudinal axisand a second leading surface of the second flute does not extend pastthe central longitudinal axis.
 12. The surgical dissection tool of claim1, wherein the leading angle surface of each flute varies by flute. 13.The surgical dissection tool of claim 4, wherein the at least one rakesurface is in front of a plane through the central longitudinal axis.14. The surgical dissection tool of claim 1, wherein the first rakesurface and a first relief surface of the first flute forms a firstangle; and a first leading angled surface of the first flute and thefirst rake surface form a second angle substantially the same as thefirst angle.
 15. A surgical dissection tool for cutting bone and othertissue, comprising: a shank; and a cutting head extending from theshank, the cutting head and the shank having a central longitudinalaxis, the cutting head having an outer surface with three flutes formedtherein, each flute comprising: a rake surface intersecting the outersurface to form a cutting edge; a relief surface opposite the rakesurface; and a leading angled surface extending from the relief surfaceto a distal end portion of the outer surface; wherein a shape of eachflute varies from each other.
 16. The surgical dissection tool of claim15, wherein a length of the cutting edge of each of the flutes differsamong the flutes.
 17. The surgical dissection tool of claim 15, whereina surface area of each rake surface varies from each flute.
 18. Thesurgical dissection tool of claim 15, wherein at least one rake surfaceis parallel to, but offset from a plane through the central longitudinalaxis.
 19. A surgical dissection tool for cutting bone and other tissue,comprising: a shank; and a cutting head extending from the shank, thecutting head and the shank having a central longitudinal axis, thecutting head having an outer surface with an odd number of flutes formedtherein, each flute comprising: a rake surface intersecting the outersurface to form a cutting edge; a relief surface opposite the rakesurface; and a leading angled surface extending from the relief surfaceto a distal end portion of the outer surface; wherein a first leadingangled surface of a first flute extends past the central longitudinalaxis and a second leading angled surface of a second flute does notextend past the central longitudinal axis.
 20. The surgical dissectiontool of claim 19, wherein an end view of the dissection tool defines areference boundary that intersects the cutting edge and a cam surfaceforms a cam relief between the cam surface and the reference boundary.